1. Field of the Invention
The present invention relates to an apparatus for removing noise, and more particularly, to an apparatus for removing noise capable of removing blocking discontinuity noises and ringing noises.
2. Description of the Related Art
The recent development in digital video technology has resulted in the improvement of electric home appliances such as a digital camera, a mobile camera, a DVD player and a digital broadcasting system. However, blocking discontinuity noises and ringing noises are caused in these systems due to the emphasis of color contrast in images, the increase in the entire luminance of images, or the post-treatments such as enlargement and reduction of an image in size, and filtering processes.
For these blocking discontinuity noises, a grid noise occurs in relatively similar areas between the pixels, and a staircase effect appears in the form of staircase along interfaces of images.
The ringing noise occurs from the truncation due to the quantization of data, and therefore pictures appear as if they are overlapped in many folds due to this ringing noise.
In general, a lowpass filter is used in the conventional methods for removing a blocking discontinuity noise and a ringing noise. However, the conventional methods have a problem that blurring noises are caused since high-frequency components are degraded in the entire images. As an alternative for removing a ringing noise, there is a method for removing a ringing noise comprising: detecting an area having a ringing noise according to the results of local statistics, adaptively (optionally) selecting an exclusive low pass filter and employing the exclusive low pass filter. However, the method has a problem that all values in a corresponding area are processed since the characteristics of algorithm require the statistics. Therefore, the method requires large amounts of time since an arithmetic operation is complicated and repeatedly performed, and pixels in the entire image should be processed one by one. In addition, since the exclusive low pass filters are manufactured previously, stored and extracted for use (ROM mode), it is difficult to precisely control active changes and values with increasing precision.